Rarefied gas flows through the circular tubes with a finite length were numerically simulated by the Direct Simulation of Monte Carlo method. The effects of boundary conditions, such as accommodation coefficients and surface temperatures at the solid surfaces of the tubes are discussed. The rarefied gas flows covered are the range from rough vacuum to extremely high vacuum conditions. According to the results of free molecular flow, the transmission probabilities increase with decreasing momentum accommodation coefficients. On the other hand, the probabilities increase with decreasing the surface temperatures.